Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F214/18—Monomers containing fluorine
  • C08F214/26—Tetrafluoroethene
  • C08F214/262—Tetrafluoroethene with fluorinated vinyl ethers

Definitions

• the invention relates to copolymers consisting of tetrafluoroethylene, perfluoro(alkyl vinyl) ethers and hexafluoropropene and to a process for their manufacture.
• polytetrafluoroethylene which has been known for over 30 years, has been able to win a special position in the plastics market.
• properties such as high thermal stability, high melting point, resistance to all customary chemicals, low coefficient of friction, extreme anti-adhesion properties and also excellent mechanical and electrical properties make polytetrafluoroethylene a construction material which is today indispensible and for which in many fields of application there is no substitute.
• Perfluorinated or at least partially fluorinated comonomers meet this requirement best. It is thus possible to produce copolymers that are on the one hand plastics that are similar to polytetrafluoroethylene and on the other hand can be processed like normal thermoplasts by conventional methods, that is to say on extruders, blown film machines and injection molding machines, on calenders, and in accordance with other current techniques.
• copolymers of this type which have become very important industrially and on account of their favourable properties have obtained an important position in the market, are the copolymers of tetrafluoroethylene (abbreviated to TFE hereinafter) and hexafluoropropene (HFP hereinafter) as well as, recently, copolymers of TFE and fluorinated alkyl vinyl ethers and of these especially those with perfluorinated alkyl vinyl ethers (PAVE hereinafter). From a particular HFP or PAVE content these copolymers are true thermoplasts. Their resistance to chemicals is equal to that of polytetrafluoroethylene. The same applies, with certain limitations, as regards the mechanical and electrical properties.
• the melting point of these copolymers is in the case of TFE/HFP copolymers approximately 50° to 80° C. and in the case of TFE/PAVE copolymers approximately 20° to 25° C. below that of polytetrafluoroethylene at a molecular weight adjustment correct for the processing.
• the maximum continuous use temperature in the case of the former copolymer is reduced by 50° to 60° C., and in the case of the latter only by approximately 10° C. In addition, the latter also have a better tensile strength and dimensional stability under heat and a slightly higher hardness.
• copolymers of TFE and HFP can be produced from appropriate comonomer mixtures by radical-controlled copolymerization, wherein to obtain suitable processing properties the content of HFP comonomer in the comonomer mixture must be at least 25% by weight (U.S. Pat. No. 2,549,935), and preferably 30 to 90% by weight (U.S. Pat. Nos.
• the polymerization can be carried out in an aqueous medium (U.S. Pat. Nos. 2,549,935; 2,946,763 and 3,132,124), in a non-aqueous medium (U.S. Pat. Nos. 2,952,669 and 3,062,793), in an aqueous phase with emulsified perfluorocarbon solvent therein (U.S. Pat. No. 2,952,669), at high (U.S. Pat. No. 3,062,793) as well as at low temperatures (U.S. Pat. No. 2,598,283).
• TFE/HFP copolymers that meet the exacting requirements as regards processing properties and properties in use must have an HFP content of between 7 and 27% by weight, as normally determined by the net absorption ratio of the two IR bands at 983 cm -1 and 2353 cm -1 (corresponding to values of this absorption ratio of 1.5 to 6).
• TFE/HFP copolymers with an HFP content of less than 7% by weight are too crystalline, too fragile and too brittle and are, therefore, not capable either of being processed or used.
• Products having an HFP content of more than 27% by weight (IR net absorption ratio >6) have relatively good mechanical properties but the melting point lies in a very low range of a little over 200° C. down to approximately 150° C. Also the ease with which they swell or dissolve in organic solvent is much increased. Such products are therefore only of secondary importance.
• the copolymers thus produced have a number of disadvantages, however, especially a highly fluctuating molecular weight which is difficult to control with consequent markedly varying melt viscosities. Unstable end groups are responsible for the occurence of bubbles in molded articles produced therefrom and these bubbles considerably impair the mechanical strength. A very wide molecular weight distribution is the reason for the marked and unacceptable swelling of the extruded or injection-molded articles, making it almost impossible to produce molded articles that are dimensionally accurate. Furthermore, molded articles of this type may shrink excessively if exposed to elevated temperatures.
• Chain transfer agents of this type are especially hydrogen and lower hydrocarbons such as methane or ethane.
• copolymerization in the aqueous phase is preferred to one carried out in a purely organic solvent since this enables the awkward and expensive recovery of four to ten times the amount of special and expensive highly fluorinated solvents calculated in the copolymer, to be dispensed with.
• copolymer dispersions that can be produced only in aqueous medium are highly desirable for many industrial purposes such as, for example, for coatings, impregnation, dip coatings, composite adhesion and the like.
• 3,635,926 does not provide an industrially favourable solution since the advantage of being able to polymerize in aqueous phase is limited as a result of the fact that the recirculation and reseparation of the comonomers used in excess is rendered difficult by the presence of gaseous chain transfer agents. Furthermore it is stated therein that the polymerization rate is reduced by the gaseous chain transfer agents used so that it is extremely desirable, in order to increase it, to add a certain amount of a fluoroalkane or fluorochloroalkane solvent to the aqueous phase.
• thermoplastic fluorocopolymer which renders possible a rational and economic use of the valuable comonomers.
• Another object of this invention is to provide a thermoplastic fluorocopolymer with properties similar to those of polytetrafluoroethylene which should furthermore have favourable processing properties and end use properties.
• the present invention lies in a process for the copolymerization of tetrafluoroethylene with 1 to 6 mole %, calculated on the total amount of comonomers added, of a perfluoro(alkyl vinyl) ether of the formula
• n is an integer of between 1 and 3, in the presence of radical-forming catalysts and chain-transfer agents at pressures of 3 to 50 atmospheres gauge and temperatures of +10 to +150° C., optionally also in the presence of emulsifiers and buffer substances, wherein the copolymerization is carried out with the addition of 25 to 5 mole %, calculated on the total quantity of comonomers added, of hexafluoropropene, in the presence of a liquid chain-transfer agent in aqueous phase.
• Perfluoro(propyl vinyl) ether (referred to as PPVE hereinafter) is especially preferred. Mixtures of the mentioned fluoroalkylperfluorovinyl ethers may also be used as comonomers.
• the copolymerization is started under free radical-forming conditions. These can be achieved by either a penetrating, high-energy radiation or by water-soluble, radical-forming catalysts, as known in large number by those skilled in the art for the polymerization and copolymerization of tetrafluoroethylene. Catalysts of this type are in particular peroxidic compounds.
• hydrogen peroxide its salts such as sodium or barium peroxide
• its addition compounds with borates, carbonates and urea and its diacyl derivatives such as, for example, diacetyl peroxide, dipropionyl peroxide, dibutyryl peroxide, dibenzoyl peroxide, benzoylacetyl peroxide, disuccinic acid peroxide, diglutaric acid peroxide, and dilauroyl peroxide.
• Water soluble per-acids such as peracetic acid, as well as its water-soluble salts (especially ammonium, sodium and potassium salts) or its esters, such as, for example, tert.-butylperoxyacetate and tert.-butylperoxypivalate, may also be mentioned. It is also possible to use the water-soluble salts, especially ammonium, potassium and sodium salts, of other per-acids, such as peroxymonosulfuric aced and peroxydisulfuric aced, and optionally also perphosphoric acid. Also suitable are perfluoroacyl peroxides or ⁇ -hydrofluoroacyl peroxides.
• a further useful class of catalysts comprises certain water-soluble azo compounds, such as those described, for example, in U.S. Pat. Nos. 2,471,959, 2,515,628 and 2,520,338. Particularly in the lower temperature range it is possible to use as catalyst the known and very effective redox systems, which produce radicals at an adequate rate at temperatures of between 10° to 50° C.
• the quantity of catalyst added is between 0.03 and 2% by weight, preferably between 0.05 and 1% by weight, calculated on the total quantity by weight of the comonomers used.
• the total quantity of catalyst may be added to the polymerization liquor at the beginning of the reaction. In the case of relatively large batches it may, however, be advantageous to feed in the total quantity of catalyst continuously during the course of polymerization until a conversion of 70 or 80% is reached. It is likewise possible for a portion of the catalyst quantity to be present from the beginning and for the rest to be fed in all at once or in portions.
• the addition of accelerations for example, soluble salts of iron, of copper and of silver can be advantageous, especially when using redox systems as catalysts.
• the pH value of the liquor at the beginning of polymerization should advantageously be in the range of from 3 to 10, preferably in the range of from 4 to 9.
• the copolymerization of the three monomers can be carried out either according to the suspension polymerization process or according to the emulsion polymerization process.
• suspension polymerization the necessary weakly acidic or weakly alkaline pH range is established by the addition of suitable buffer substances to the aqueous liquor.
• buffers for the acidic range which generally simultaneously act as precipitants, include ammonium chloride, ammonium dihydrogenphosphate, boric acid, and ammonium oxalate, and also mixtures of such compounds.
• buffer substances for the alkaline range include, borax, ammonium carbonate, ammonium hydrogen carbonate, ammonium carbamate, ammonium pentaborate or even ammonia itself.
• emulsifiers of the type described hereinafter, in order to avoid the formation of lumps, to prevent coating forming on the vessel and to obtain a relatively uniform particle size.
• the quantity by weight of such emulsifiers is in this case generally below 150 ppm, preferably below 550 ppm, calculated on the aqueous liquor present at the beginning of the polymerization process.
• emulsifiers must be added to the liquor in a quantity of approximately 0.01 to 3% by weight preferably 0.03 to 1.5% by weight, calculated on the liquor used.
• emulsifiers familiar to those skilled in the art for the emulsion polymerization of fluoroolefins can also be used for the process according to the invention.
• Suitable emulsifiers are ammonium and alkali metal salts of relatively long-chained perfluorocarboxylic acids and of ⁇ -hydrofluorocarboxylic acids, particularly those having 6 to 12 carbon atoms.
• salts of perfluorocaproic, perfluorocaprylic, perfluorocapric, and perfluorolauric acid may be mentioned as examples the salts of perfluorocaproic, perfluorocaprylic, perfluorocapric, and perfluorolauric acid, as well as those of the corresponding ⁇ -hydrofluorocarboxylic acids. It is equally possible to use as emulsifiers the salts of perfluoroalkylsulfonic acids and perfluoroalkylphosphonic acids of the same C-chain lengths.
• the salts of perfluoroalkoxypropionic acids, especially perfluoropropoxypropionic acid may be mentioned as an example of a further class of extremely effective emulsifiers.
• the emulsifiers mentioned may also be used in the form of the free acids and optionally neutralized with ammonia, in which case the ratio of acid and ammonia can also be used to adjust the pH value.
• Suitable chain transfer agents are aliphatic carboxylic acid esters, ketones, alcohols or ether alcohols, such as, for example, acetone, methanol, ethanol, isopropanol, malonic esters or lower dialkylglycol, such as diethyleneglycol or dipropyleneglycol; also halogenated derivatives from these compound groups, such as bromoacetic esters, or bromomalonic esters, bromoacetone, as well as chloromethanol or bromomalonic esters, bromoacetone, as well as chloromethanol or bromomethanol and chloroethanol or bromoethanol.
• saturated aliphatic halohydrocarbons that contain as halogens fluorine, chlorine and/or bromine, and optionally also contain hydrogen, are used as liquid chain transfer agents.
• X can be F, Cl, Br, H in any combination, provided that the number of F atoms per molecule is a maximum of 2 m+1, preferably a maximum of 2, the number of H-atoms is a maximum of 2 m+1 and the number of Br atoms is a maximum of 4.
• halohydrocarbons tetrachloroethane, trichloroethane, hexachloropropane, tetrafluorodibromoethane and chlorodibromotrifluoroethane; especially preferred are chloroform, methylene chloride and carbon tetrachloride.
• Suitable chain transfer agents should be liquid at room temperature (20° C.) and normal pressure, they should be adequately soluble in water and they should bring the swelling rate of the terpolymer to the required range suitable for processing.
• the quantity of the mentioned liquid chain transfer agents used depends on the intensity of their regulating action, which is known to those skilled in the art, and will be in the range of from 0.02 to 5% by weight calculated on the liquor used. In the case of the preferred halohydrocarbons, 0.05 to 3, preferably 0.1 to 1.5% by weight of liquid chain transfer agent is used, calculated on the liquor. If desired, mixtures of such liquid chain transfer agents can be used.
• the necessary amount of chain transfer agent is advantageously added before polymerization begins. In the case of quickly reacting chain transfer agents it may, however, be advisable to start with a portion and then feed in the rest continuously or discontinuously during copolymerization.
• the copolymerization process according to the invention is advantageously carried out under slightly elevated pressure because of the low solubility of TFE in water; a pressure of 3 to 50 atmospheres gauge is generally sufficient. For reasons concerning safety and costs it is desirable to operate at the lowest possible pressures. As a compromise as regards adequate economy and favourable space-time yields a pressure of approximately 8 to 18 atmospheres gauge has proved most favourable for the copolymerization.
• the polymerization temperature can, depending on the type of catalyst selected, be in the range of between +10° and +150° C.
• temperatures in the lower part of this temperature range are chosen, that is preferably between 10° and 50° C. and especially between 20° and 40° C.
• anticoagulants such as longer chained paraffin hydrocarbons, paraffin waxes or white oils, which should be liquid under the polymerization conditions
• other dispersion stabilizers in small amounts ( ⁇ 100 ppm), such as polyglycol ethers or polyglycol esters of fatty acids.
• the copolymerization according to the invention proceeds for example in the following way.
• the constituents mentioned as follows are placed in a suitable polymerization vessel, which consists, for example, of steel or some other acid-resistant alloy, and if desired is enamelled on the inside: the reaction medium that is an appropriate amount of demineralized water, in the case of suspension polymerization the desired amount of buffer substance or precipitant, in the case of emulsion polymerization the desired amount of emulsifier and optionally anticoagulant, and also, if necessary, a small amount of accelerator in the form of an aqueous solution of the appropriate metal salt. Then the liquid chain transfer agent and, if using a redox catalyst, one of the two components of the redox pair, are added.
• HFP and the respective PAVE are introduced into the vessel preferably in liquid form, and the TFE is advantageously introduced by way of a gas chamber. All three momoners are preferably introduced separately, but it is possible to introduce mixtures of two or of all three monomers.
• the total monomer mixture introduced into the reactor should, gross, have approximately the following composition:
• the total quantity of TFE can be introduced at the beginning of the polymerization process. It is more advantageous, however, to introduce 10 to 50% of the required quantity of TFE in the starting mixture of monomers and for feed the remaining quantity into the gas space continuously or in portions in the course of the polymerization process.
• the total quantity of catalyst, or a portion thereof is added to the liquor by means of a suitable feeder. The addition of the catalyst to the original liquor and its subsequent addition is best carried out in the form of dilute solutions.
• the pressure in the polymerization reactor can, if subsequently feeding in a portion of the TFE quantity, be kept constant by controlling the introduction in accordance with the measure of consumption. Under certain circumstances it can also be advantageous subsequently to feed in a portion of one of the two or of both other monomers during the course of the polymerization, either continuously or discontinuously.
• the copolymerization is continued until the liquor has a solids content of up to approximately 30% by weight, preferably of 10 to 25% by weight. Thereinafter the supply of the monomer or monomers and optionally the supply of auxiliaries is stopped and the pressure in the vessel can be reduced by subsequently polymerizing down. The monomer mixture that finally remains is slowly blown off and optionally completely removed from the liquor at elevated temperature or reduced pressure, and by means of fractional condensation, or total condensation with subsequent fractional redistillation, separated into the starting components again. Consequently losses of the valuable monomers are almost completely avoided.
• the polymerization liquor which contains the suspended or dispersed terpolymer, is then drawn off and worked up in the usual manner.
• the suspended particles similar to a fine grit, are separated from the liquor by a sieve or a filter, carefully washed with demineralized water, and depending on the intended use, pulverized or granulated.
• the product is then dried, tempered and optionally melt-granulated.
• the very transparent, bluish-white dispersion resulting from the emulsion polymerization contains the solid in the form of spherical particles having a mean particle diameter of 0.03 to 0.5, preferably 0.1 to 0.3 ⁇ m, and having a narrow size distribution, expressed by the value ⁇ d 1/2 /d av 0.35.
• This value ⁇ d 1/2 /d av is derived from the particle diameter distribution curve.
• the curve is produced by counting the particle diameters that can be measured in the electron-microscopic scan of the dispersion. In this the abscissa value associated with the curve maximum corresponds to the size d av .
• a straight line is placed through the middle of the corresponding ordinate value parallel to the abscissa axis, and the distance lying between the points of intersection of this straight line with the two branches of the distribution curve is indicated by ⁇ d 1/2 .
• ⁇ d 1/2 /d av for the size distribution is between >0.20 and ⁇ 0.35.
• the copolymerization process of the invention can be advantageous to conduct the copolymerization process of the invention according to the emulsion process as a seed polymerization process, that is a certain quantity of a dispersion produced according to the process of the invention is added at the beginning with the liquor to a polymerization mixture, and then the three monomers are polymerized as described.
• the seed quantity (expressed as solid substance) is advantageously between 1 and 10% by weight, preferably between 2 and 8% by weight, calculated on the quantity of solid in the end dispersion.
• the dispersions obtained have an excellent stability and exhibit a favourable settling behaviour. They may subsequently be further stabilized with non-ionic, surface-active dispersing agents, such as, for example, oxalkylated, especially oxethylated alkyl phenols or alternatively polyoxalkylates, and concentrated in this form to higher solid contents for example of 30 to 60% by weight, by known methods.
• non-ionic, surface-active dispersing agents such as, for example, oxalkylated, especially oxethylated alkyl phenols or alternatively polyoxalkylates
• the terpolymer dispersion obtained according to the process of the invention can be processed as dispersions or coagulated by adding coagulants such as, for example, electrolyte salts or organic solvents, such as acetone, or also by applying shearing forces, for example by stirring, whereby a solid coagulated powder is separated from the liquor and can be worked up in the usual manner.
• coagulants such as, for example, electrolyte salts or organic solvents, such as acetone
• the polymer is to be further processed in the solid state, it is advantageous first of all to dry it at a high temperature of up to approximately 250° C. and then to temper it for a few hours at approximately 280° C.
• perfluorinated alkylvinyl ethers such as for example, perfluoro (propyl vinyl) ether, used as comonomers are as is known, produced only by complicated multi-stage processes and are, therefore, extremely costly substances and so the slightest loss of these substances must be avoided as far as possible.
• the pressure was 16 atmospheres, the temperature 30° to 31° C. Otherwise the polymerization conditions corresponded to those in Example 2 (see below).
• the table shows that without the addition of HFP to the comonomer mixture the rate of incorporation of the perfluoro(propyl vinyl) ether into the copolymer is at the extremely low value of 1.1% by weight, and increases only to an insignificant extent with the addition of small amounts of HFP.
• the rate of incorporation of the perfluoro(propyl vinyl) ether into the copolymer is at the extremely low value of 1.1% by weight, and increases only to an insignificant extent with the addition of small amounts of HFP.
• an HFP proportion of 5 to 30 mole % an increase of about 100% and more is observed, whereas at high proportions of HFP the rate of incorporation of the perfluoro(propyl vinyl) ether falls back practically to its initial value.
• the incorporation of HFP into the terpolymer increases continuously in this range.
• the copolymerization process according to the invention provides the following principal advantages:
• another embodiment of the present invention resides in a non-elastic, thermoplastic terpolymer, which comprises in copolymerized form, wherein the proportions are calculated on the total amount of monomer content and expressed in mole percent (and corresponding weight %), of
• melt flowing index (MFI) value 0.1 to 200 g/10 min, measured at 372° C. under a piston load of 5000 grams according to ASTM D 1238-65-T.
• a preferred composition of the terpolymer according to the invention comprises in copolymerized form, expressed in mole % (weight %), of 96.3 to 99.4 mole % (92.55 to 98.75 weight %) of TFE, 1.8 to 0.3 mole % (2.6 to 0.45 weight %) of HFP and 1.9 to 0.3 mole % (4.85 to 0.8 weight %) of a PAVE of the above formula.
• a composition of the terpolymer comprising 96.3 to 98.9 mole % (92.55 to 97.55 weight %) of TFE, 1.8 to 0.3 mole % (2.6 to 0.45 weight %) of HFP and 1.9 to 0.8 mole % (4.85 to 2.0 weight %) of a PAVE of the formula given above.
• the terpolymers may contain mixtures of the PAVE monomers of the formula given above in copolymerized form.
• Preferred PAVE is the perfluoro(propyl vinyl) ether.
• the terpolymers according to the invention have a melt flowing index (MFI) value of 0.5 to 50 g/10 min (using the same measuring conditions).
• the terpolymers according to the invention of the above composition and having the given melt index values are obtainable by the above-described copolymerization process of the invention.
• the terpolymers as characterized by the said composition and the MFI values given, have the following characteristic properties:
• the density lies in the range of from 2.1 to 2.2, preferably 2.12 to 2.18. It varies slightly, depending on the HFP and PAVE content of the terpolymer concerned.
• the melting point is dependent to a greater extent than the density on the composition of the terpolymer and furthermore on the respective adjustment of the MFI value.
• the melting points of the terpolymers according to the invention are in the range between 290° and 320° C., preferably in the range between 300° and 316° C.
• the terpolymer produced according to Example 1 according to the curve of differential thermoanalysis, has a commencing melting point of 275° C., a melt maximum of 305° C. and the melting range ends at 327° C.
• Thermal decomposition of the terpolymers is not discernible before a temperature of 400° C., preferably not before 430° C.
• the so-called swelling rate of such thermoplastically processable copolymers is usually defined by the ratio of the diameter of the extruded strand extruded from the melt index testing apparatus and measured after cooling to room temperature at a point 1 cm from the beginning of the strand, to the diameter of the nozzle of this testing apparatus.
• the said ratio should advantageously be close to 1, which indicates complete correspondence between the dimensions of the molded strand and of the mold. Larger deviations above (swelling) or below (contraction) are extremely undesirable in practice since they impair the production of dimensionally accurate molding articles. Frequently this swelling rate D extrudate /D nozzle (ratio of the diameters) is also quoted in the form of the percentage deviation (swelling rate -1) 100.
• the ideal value here is zero, positive numbers indicate a "percentage swelling", negative numbers a "percentage contraction".
• values of the percentage swelling of up to 30 or up to 20%, still tolerable for practical processing could only be achieved in the aqueous-phase copolymerization process with the use of gaseous chain transfer agents.
• the terpolymers according to the invention produce swelling rates that may lie between 0.8 to 1.2, but preferably lie between 0.85 and 1.1, and especially between 0.90 and 1.0. This corresponds to values for percentage contraction and percentage swelling of between -20% to +20% at a point 1 cm from the beginning of the strand, but preferably between -15 and +10% and especially between -10 and ⁇ 0%.
• the terpolymers according to the invention also show some improvements when used as insulating materials for electrical wires.
• Table VIII shows comparative measurements of some electrical properties. It was also found that wire coverings made of the terpolymers according to the invention have an improved elongation at break.
• the terpolymers according to the invention are absolutely comparable with the known copolymers of TFE and fluorinated alkylvinyl ethers. This applies in particular to the transparency, the ball indentation hardness and the Shore D hardness, the Vicat value, the ultimate bending stress, the severance strength, and also to the resistance to chemical attack. The intrinsic viscosity curve and the flow behaviour are similar.
• the determination of the density is carried out according to the buoyancy method.
• the test body, suspended on a perlon thread approximately 10 ⁇ m thick, is first of all weighed in air, then the reduction in weight on immersion in butyl acetate is ascertained.
• a testing apparatus according to ASTM-Standard D-1238-65 T is used, in which, however, the melting cylinder, piston and outlet nozzle are made of a corrosion-resistant material.
• the outlet opening of the 8 mm long nozzle has a diameter of 2.0955 mm.
• the diameter of the cylinder is 0.95 cm.
• a certain quantity of polymer is melted in the cylinder at a constant temperature of 372° C. and to compensate for differences in temperature is left for 10 minutes. Then the melt is extruded through the outlet opening of the nozzle with a piston load of 5000 g.
• melt flowing index (MFI) value (i 5 , 372° C.) is quoted by the quantity of substance in grams emerging within 10 minutes.
• MFI melt flowing index
• Silvered copper wires of the type AWG 22/7 were used for wire-covering. This operation was carried out on a wire extruder with a draw-off speed of 50 m/min. The temperature of the composition was 331° C. in the feed in zone and 382° C. in the extruder head. The thickness of the insulation was 250 ⁇ m, corresponding to a total wire thickness of 1.26 mm.
• the content of PAVE and HFP in the terpolymer according to the invention is determined from the infrared spectra, measured in 25 ⁇ m thick molded films on the IR spectrometer Perkin-Elmer 521.
• the ether content is obtained directly in % by weight if the net absorption of the characteristic band of the PAVE used is related to a reference band at 2353 cm -1 and multiplied by a factor in line with the respective molecular weight of the ether. In the case of perfluoro(propyl vinyl) ether, this characteristic band is at 993 cm -1 and the multiplication factor is 0.95.
• the HFP content is determined in an analogous manner.
• the net absorption ratio of the characteristic HFP band (983 cm -1 ) and the reference band (2353 cm -1 ) is calculated and multiplied, in this instance by 4.5, which gives the HFP content in % by weight.
• the characteristic band of the ether lies so close to the HFP band that there is considerable overlapping, and one or other of the two bands appears in the IR spectrum only as a shoulder. In order, in such cases, to arrive at an accurate determination of the content, the spectra of a number of mixtures of bipolymers were taken.
• mixtures of a TFE-HFP copolymer (HFP content 4.7% by weight, determined as 2.28% by weight, determined as described above) were produced in a number of different compositions.
• the IR spectra were taken from molded films of these mixtures and evaluated, and from the results calibration curves for the exact evaluation for the terpolymer spectra were obtained.
• the terpolymers according to the invention can be mixed in any proportions in the form of powders, granules and dispersions with processing auxiliaries, such as the usual filters, pigments and dyestuffs.
• processing auxiliaries such as the usual filters, pigments and dyestuffs.
• inorganic fillers or pigments such as glass (in the form of powder, beads, flakes or fibers), ceramics, coke, graphite, carbon black, silica and silicates of all kinds, for example, asbestos, mica, talcum, quartz powder, and also metal sulfides and metal oxides, for example, of iron, cobalt, cadmium and chromium, as well as powders of metals and alloys, such as, for example, bronze, copper, aluminium, iron, silver and titanium.
• the terpolymers according to the invention are extremely well suited to processing by all conventional methods for the processing of thermoplastic synthetic materials. Examples of such processing methods include the extrusion of strands, profiles, tubes, flat films and blown films, also injection molding processes, calendering films and webs, but also compression molding to form shaped articles of any kind. It is particularly advantageous in a thermoplastic processing method of this type that the terpolymers according to the invention exhibit a very low tendency to the formation of fractures over the entire MFI value range quoted (and over the range of the content of PAVE) and that furthermore, in comparison with copolymers of TFE/PAVE of a comparable melt viscosity, can be processed at temperatures approximately 20° to 40° C. lower.
• the terpolymers according to the invention are advantageously brought into a form suitable for processing (granules, pellets, lentils and the like).
• products and commodity goods that can be produced from the terpolymers of the invention according to the processing methods mentioned, for example, fibers, filaments, films, webs, plates, wire and cable insulation, sliding elements and sealing elements of all kinds, such as piston pin bushings, gaskets and the like, switch segments, pipes and tubes for all purposes, parts of laboratory apparatus, non-conductors for capacitors, woven textile or non-woven fleeces.
• the terpolymers according to the invention can be used with advantage for coating, impregnating or steeping threads, woven textiles, non-woven fleeces, and also for covering and coating molded bodies and surfaces made of other synthetic materials and other materials such as ceramics, glass and metals. Coating or lamination using the terpolymers according to the invention provides surfaces and articles treated in this manner with protection against corrosive attack by other media, and optionally also imparts increased resistance to temperature. A further use is as an intermediate layer when gluing or welding surfaces or molded bodies of polytetrafluoroethylene or of other fluoropolymers to themselves or to other materials.
• 73 l demineralized water are introduced into a polymerization reactor enamelled on the inside, provided with an impeller stirrer and having a total empty volume of 194 l, and 100 g of perfluorooctanoic acid and 28 ml of ammonia (18% by weight in H 2 O) as well as 50 g ammonium hydrogen oxalate are dissolved therein.
• the stirring speed is then reduced to 140 to 150 r.p.m. and polymerization is started by constantly pumping in a 1.5% by weight aqueous KMnO 4 solution at a speed of 30 cm 3 /min.
• 150 ml of concentrated HCl are added to the dispersion and stirring is carried out with a high-speed propeller stirrer until the solid material has separated from the aqueous phase.
• the flaky powder removed by stirring is washed 6 times, while stirring vigorously, with 80 l of demineralized water each time, then separated from the water and dried in the drying chamber under nitrogen at 200° C. for 10 to 12 hours, and finally tempered for a further 8 to 10 hours at 270° to 280° C.
• the melting point maximum determined from the differential thermoanalysis is 305° C.
• the terpolymer has a melt flowing index value of 16 g/10 min at 5 kg load and 372° C., determined as described above, and a swelling rate, measured 1 cm from the beginning of the strand from the melt flowing index testing apparatus, of 0.82, representing a percentage concentration of 18%.
• PPVE poly(ethylene glycol)
• 4.5 g were incorporated in each 100 g of polymer, that is a total of 441 g or 44.25% of the monomeric PPVE used.
• 440 g were recovered, that is, 82.4% of the unreacted monomeric PPVE.
• the product exhibited the following properties: density 2.149; tear strength of the ASTM injection molded tension test bar (23° C.) 19.9 N/mm 2 , its yield stress (23° C.) 17.5 N/mm 2 , its elongation at break (23° C.) 160%; tear strength of a molded film 26.4 N/mm 2 , its elongation at break 430%; weight loss after treatment at 280° C. for more than 1000 hours 0.85% by weight, and at 280° C. for more than 2000 hours 0.94% by weight.
• the copolymerization was carried out in the same manner as that described in Example 1, but without the addition of HFP.
• the total monomer mixture accordingly had a composition of 2.6 mole % of PPVE and 97.4 mole % of TFE.
• the copolymer of PPVE and TFE obtained had a PPVE content of 1.7% by weight determined by IR spectroscopy. With the same concentration of 13 g of PPVE per liter of liquor, in this case only 1.7 g of PPVE were incorporated in 100 g of copolymer compared with 4.5 g in Example 1.
• the temperature of the liquor is controlled at 27° to 30° C. and the stirring is reduced again to 200 r.p.m.
• Polymerization is started by pumping in a 1.5% by weight aqueous solution of K 2 MnO 4 and the supply of this initiator solution is maintained at 33 ml/min over the entire duration of polymerization.
• a further 4300 g (43 mole) of TFE are added in the course of 60 minutes. After this time the pressure drop to 7 atmospheres gauge is awaited, then, in order to recover the three monomers, the pressure is relaxed and the monomers, as described in Example 1, are subjected to fractional condensation.
• the total monomer mixture accordingly has the following composition:
• the dispersion formed in a quantity of 28.5 kg and having a solids content of 15.8% by weight (that is 4.5 kg of terpolymer) is drawn off.
• the dispersion prepared in this manner is then concentrated in vacuo to a solids content of approximately 50% by weight by the removal of water in a circulation evaporator. The dispersion is stable for a long time in this form.
• the terpolymer formed has according to the IR-spectroscopic methods of determination described, the following composition:
• a melting point maximum of 310° C. is shown in the differential-thermoanalysis curve, and the melt flowing index value, determined as described above, is 4.7 g/10 min.
• the swelling rate was measured as 0.94, corresponding to a percentage contraction of only 6%.
• the 210 g of perfluoro(propyl vinyl)ether used correspond to a concentration of 9 g/l of liquor. Even at this lower concentration a rate of incorporation of 2.8 g per 100 g of terpolymer was achieved. Of the 84 g of unreacted PPVE, it was possible to recover 65 g, or 77.4%.
• injection molded tension test bars tear strength 16 N/mm 2 , elongation at break 190%, yield stress 16 N/mm 2 , all measured at 23° C.
• molded films tear strength 23.6 N/mm 2 , elongation at break 480%. Density: 2.152 g/cm 3 .
• TFE gaseous, HFP and PPVE liquid are introduced into the liquor.
• a total pressure of 16 atmospheres gauge is established.
• the terpolymer has an MFI value of 8 g/10 min and a swelling rate of 0.91, determined as described in Example 1.
• the total monomer mixture introduced thus comprises the following:
• the melt flowing index value of the terpolymer is 1 g/10 min, the swelling rate 1.02 (determined as described in Example 1).
• Test bars, stamped out of 2 mm thick molded films, have a tear strength (23° C.) of 23 N/mm 2 and an elongation at break of 410%.
• the polymerization is started by feeding in a 1.5% by weight aqueous solution of KMnO 4 , and this solution is metered in further in a quantity of 13 ml/min.
• Polymerization is then carried out until 7 atmospheres gauge is reached, the pressure in the reactor is relaxed and the gaseous monomers evolved are conveyed to the recovery unit.
• the liquor with the polymer suspended therein is drawn off by way of the valve in the base of the vessel and the soft, relatively large-particled suspension polymer is separated from the liquor by means of a sieve cup.
• the product is subsequently washed thoroughly several times with demineralized water, then dried for 12 hours on sheets in an oven at 200° C., and finally thermally treated at 280° C. for a further 8 hours.
• the yield is 2650 g of terpolymer in the form of a white, particulate, pourable product with the following composition:
• the terpolymer has a melt index value of 8.5 g/10 min (determined as in Example 1).

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